arXiv subjects

Geoffrey W. Marcy

Publications and source records attributed to Geoffrey W. Marcy.

At least 181 records · Page 10Linked to original sources

arXiv2008

A Jupiter-like Planet Orbiting the Nearby M Dwarf GJ832

Precision Doppler velocity measurements from the Anglo-Australian Tele- scope reveal a planet with a 9.4+/-0.4 year period orbiting the M1.5 dwarf GJ 832. Within measurement uncertainty the orbit is circular, and the minimum mass (m sin i) of the planet is 0.64+/-0.06 MJUP. GJ 832 appears to be depleted in met- als by at least 50% relative to the Sun, as are a significant fraction of the M dwarfs known to host exoplanets. GJ 832 adds another Jupiter-mass planet to the known census of M dwarf exoplanets, which currently includes a significant number of Neptune-mass planets. GJ 832 is an excellent candidate for astromet- ric orbit determination with alpha sin i = 0.95 mas. GJ 832b has the second largest angular distance from its star among radial velocity detected exoplanets (0.69 arc sec) making it a potentially interesting target for future direct detection.

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arXiv2008

Measurement of the Spin-Orbit Angle of Exoplanet HAT-P-1b

We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectra obtained during three transits exhibit the Rossiter-McLaughlin effect, allowing us to measure the angle between the sky projections of the stellar spin axis and orbit normal, λ= 3.7 +/- 2.1 degrees. The small value of λfor this and other systems suggests that the dominant planet migration mechanism preserves spin-orbit alignment. Using two new transit light curves, we refine the transit ephemeris and reduce the uncertainty in the orbital period by an order of magnitude. We find a upper limit on the orbital eccentricity of 0.067, with 99% confidence, by combining our new radial-velocity measurements with those obtained previously.

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arXiv2008

The Keck Planet Search: Detectability and the Minimum Mass and Orbital Period Distribution of Extrasolar Planets

We analyze 8 years of precise radial velocity measurements from the Keck Planet Search, characterizing the detection threshold, selection effects, and completeness of the survey. We carry out a systematic search for planets by assessing the false alarm probability associated with Keplerian orbit fits to the data. This allows us to understand the detection threshold for each star in terms of the number and time baseline of the observations, and size of measurement errors and stellar jitter. We show that all planets with orbital periods <2000 days, velocity amplitudes >20 m/s, and eccentricities <0.6 have been announced, and summarize the candidates at lower amplitudes and longer orbital periods. For the remaining stars, we calculate upper limits on the velocity amplitude of a companion, typically 10 m/s, and use the non-detections to derive completeness corrections at low amplitudes and long orbital periods. We give the fraction of stars with a planet as a function of planet mass and orbital period, and extrapolate to long period orbits and low planet masses. A power law fit for planet masses >0.3 Jupiter masses and periods <2000 days gives a mass-period distribution dN=C M^αP^βdlnM dlnP with α=-0.31 \pm 0.2, β=0.26\pm 0.1, and the normalization constant C such that 10.5% of solar type stars have a planet with mass in the range 0.3-10 Jupiter masses and orbital period 2-2000 days. The orbital period distribution shows an increase in the planet fraction by a factor of 5 for orbital periods beyond 300 days. Extrapolation gives 17-20% of stars having gas giant planets within 20 AU. Finally, taking into account differences in detectability, we find that M dwarfs are 3 to 10 times less likely to harbor a Jupiter mass planet than solar type stars.

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arXiv2007

Five Planets Orbiting 55 Cancri

We report 18 years of Doppler shift measurements of a nearby star, 55 Cancri, that exhibit strong evidence for five orbiting planets. The four previously reported planets are strongly confirmed here. A fifth planet is presented, with an apparent orbital period of 260 days, placing it 0.78 AU from the star in the large empty zone between two other planets. The velocity wobble amplitude of 4.9 \ms implies a minimum planet mass \msini = 45.7 \mearthe. The orbital eccentricity is consistent with a circular orbit, but modest eccentricity solutions give similar \chisq fits. All five planets reside in low eccentricity orbits, four having eccentricities under 0.1. The outermost planet orbits 5.8 AU from the star and has a minimum mass, \msini = 3.8 \mjupe, making it more massive than the inner four planets combined. Its orbital distance is the largest for an exoplanet with a well defined orbit. The innermost planet has a semi-major axis of only 0.038 AU and has a minimum mass, \msinie, of only 10.8 \mearthe, one of the lowest mass exoplanets known. The five known planets within 6 AU define a {\em minimum mass protoplanetary nebula} to compare with the classical minimum mass solar nebula. Numerical N-body simulations show this system of five planets to be dynamically stable and show that the planets with periods of 14.65 and 44.3 d are not in a mean-motion resonance. Millimagnitude photometry during 11 years reveals no brightness variations at any of the radial velocity periods, providing support for their interpretation as planetary.

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arXiv2007

Retired A Stars and Their Companions II: Jovian planets orbiting kappa Coronae Borealis and HD167042

We report precise Doppler measurements of two evolved stars, kappa CrB (HD142091) and HD 167042, obtained at Lick Observatory as part of our search for planets orbiting intermediate-mass subgiants. Periodic variations in the radial velocities of both stars reveal the presence of substellar orbital companions. These two stars are notably massive with stellar masses of 1.80 Msun and 1.64 Msun, indicating that they are former A-type dwarfs that have evolved off of the main sequence and are now K-type subgiants. The planet orbiting kappa CrB has a minimum mass Msini = 1.8 Mjup, eccentricity e = 0.146 and a 1208 day period, corresponding to a semimajor axis of 2.7 AU. The planet around HD167042 has a minimum mass Msini = 1.7 Mjup and a 412.6 day orbit, corresponding to a semimajor axis of 1.3 AU. The eccentricity of HD167042b is consistent with circular (e = 0.027+/-0.04), adding to the rare class of known exoplanets in long-period, circular orbits similar to the Solar System gas giants. Like all of the planets previously discovered around evolved A stars, kappa CrBb and HD167042b orbit beyond 0.8 AU.

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arXiv2007

Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest

Precision astrometry at microarcsecond accuracy has application to a wide range of astrophysical problems. This paper is a study of the science questions that can be addressed using an instrument that delivers parallaxes at about 4 microarcsec on targets as faint as V = 20, differential accuracy of 0.6 microarcsec on bright targets, and with flexible scheduling. The science topics are drawn primarily from the Team Key Projects, selected in 2000, for the Space Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities of this mission to illustrate the importance of the next level of astrometric precision in modern astrophysics. SIM PlanetQuest is currently in the detailed design phase, having completed all of the enabling technologies needed for the flight instrument in 2005. It will be the first space-based long baseline Michelson interferometer designed for precision astrometry. SIM will contribute strongly to many astronomical fields including stellar and galactic astrophysics, planetary systems around nearby stars, and the study of quasar and AGN nuclei. SIM will search for planets with masses as small as an Earth orbiting in the `habitable zone' around the nearest stars using differential astrometry, and could discover many dozen if Earth-like planets are common. It will be the most capable instrument for detecting planets around young stars, thereby providing insights into how planetary systems are born and how they evolve with time. SIM will observe significant numbers of very high- and low-mass stars, providing stellar masses to 1%, the accuracy needed to challenge physical models. Using precision proper motion measurements, SIM will probe the galactic mass distribution and the formation and evolution of the Galactic halo. (abridged)

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arXiv2007

Five Intermediate-Period Planets from the N2K Sample

We report the detection of five Jovian mass planets orbiting high metallicity stars. Four of these stars were first observed as part of the N2K program and exhibited low RMS velocity scatter after three consecutive observations. However, follow-up observations over the last three years now reveal the presence of longer period planets with orbital periods ranging from 21 days to a few years. HD 11506 is a G0V star with a planet of \msini = 4.74 \mjup in a 3.85 year orbit. HD 17156 is a G0V star with a 3.12 \mjup planet in a 21.2 day orbit. The eccentricity of this orbit is 0.67, one of the highest known for a planet with a relatively short period. The orbital period for this planet places it in a region of parameter space where relatively few planets have been detected. HD 125612 is a G3V star with a planet of \msini = 3.5 \mjup in a 1.4 year orbit. HD 170469 is a G5IV star with a planet of \msini = 0.67 \mjup in a 3.13 year orbit. HD 231701 is an F8V star with planet of 1.08 \mjup in a 142 day orbit. All of these stars have supersolar metallicity. Three of the five stars were observed photometrically but showed no evidence of brightness variability. A transit search conducted for HD 17156 was negative but covered only 25% of the search space and so is not conclusive.

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arXiv2007

Two Jovian-Mass Planets in Earthlike Orbits

We report the discovery of two new planets: a 1.94 M_Jup planet in a 1.8-year orbit of HD 5319, and a 2.51 M_Jup planet in a 1.1-year orbit of HD 75898. The measured eccentricities are 0.12 for HD 5319 b and 0.10 for HD 75898 b, and Markov Chain Monte Carlo simulations based on derived orbital parameters indicate that the radial velocities of both stars are consistent with circular planet orbits. With low eccentricity and 1 < a < 2 AU, our new planets have orbits similar to terrestrial planets in the solar system. The radial velocity residuals of both stars have significant trends, likely arising from substellar or low-mass stellar companions.

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arXiv2007

A New Planet Around an M Dwarf: Revealing a Correlation Between Exoplanets and Stellar Mass

We report precise Doppler measurements of GJ317 (M3.5V) that reveal the presence of a planet with a minimum mass Msini = 1.2 Mjup in an eccentric, 692.9 day orbit. GJ317 is only the third M dwarf with a Doppler-detected Jovian planet. The residuals to a single-Keplerian fit show evidence of a possible second orbital companion. The inclusion of an additional Jupiter-mass planet (P = 2700 days, Msini = 0.83 Mjup) improves the quality of fit significantly, reducing the rms from 12.5 m/s to 6.32 m/s. A false-alarm test yields a 1.1% probability that the curvature in the residuals of the single-planet fit is due to random fluctuations, lending additional credibility to the two-planet model. However, our data only marginally constrain a two-planet fit and further monitoring is necessary to fully characterize the properties of the second planet. To study the effect of stellar mass on Jovian planet occurrence we combine our samples of M stars, Solar-mass dwarfs and intermediate-mass subgiants. We find a positive correlation between stellar mass and the occurrence rate of Jovian planets within 2.5 AU; the former A-type stars in our sample are nearly 5 times more likely than the M dwarfs to harbor a giant planet. Our analysis shows that the correlation between Jovian planet occurrence and stellar mass remains even after accounting for the effects of stellar metallicity.

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arXiv2007

Spin-Orbit Alignment for the Eccentric Exoplanet HD 147506b

The short-period exoplanet HD 147506b (also known as HAT-P-2b) has an eccentric orbit, raising the possibility that it migrated through planet-planet scattering or Kozai oscillations accompanied by tidal dissipation. Either of these scenarios could have significantly tilted the orbit relative to the host star's equatorial plane. Here we present spectroscopy of a transit of HD 147506b, and assess the spin-orbit alignment via the Rossiter-McLaughlin effect. We find the sky projections of the stellar spin axis and orbital axis to be aligned within 14 deg. Thus we find no corroborating evidence for scattering or Kozai migration, although these scenarios cannot be ruled out with the present data.

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arXiv2007

Role of Dynamical Research in the Detection and Characterization of Exoplanets

(Abridged) The discovery of extrasolar planetary systems revealed an unexpected diversity of planetary systems that has revolutionized planet formation theory. A strong program of theoretical research is essential to maximize both the discovery potential and the scientific returns of future observational programs, so as to achieve a deeper understanding of the formation and evolution of planetary systems. We outline three broad categories of theoretical research: detailed studies of specific planetary systems, testing planet formation models by comparing their predictions to the observed exoplanet population, and detailed modeling of specific physical processes. We describe how such theoretical research plays an important role in analyzing observations for a wide range detection methods and contributes to understanding the Earth's place in the universe and the potential for Earth-like life beyond our solar system. In this white paper, we suggest how to maximize the scientific return of future exoplanet observations. Our recommendations include a strong theory program, support for multiple observational programs that will study a diverse set of planets and stars, significant observing time devoted to follow-up observations, and healthy collaboration between observers and theorists.

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arXiv2007

Fourteen New Companions from the Keck & Lick Radial Velocity Survey Including Five Brown Dwarf Candidates

We present radial velocities for 14 stars on the California & Carnegie Planet Search target list that reveal new companions. One star, HD 167665, was fit with a definitive Keplerian orbit leading to a minimum mass for the companion of 50.3 Mjup at a separation from its host of ~5.5 AU. Incomplete or limited phase coverage for the remaining 13 stars prevents us from assigning to them unique orbital parameters. Instead, we fit their radial velocities with Keplerian orbits across a grid of fixed values for Msini and period, P, and use the resulting reduced chi-square surface to place constraints on Msini, P, and semimajor axis, a. This technique allowed us to restrict Msini below the brown dwarf -- stellar mass boundary for an additional 4 companions (HD 150554, HD 8765, HD 72780, HD 74014). If the combined 5 companions are confirmed as brown dwarfs, these results would comprise the first major catch of such objects from our survey beyond ~3 AU.

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arXiv2007

Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants

We report precision Doppler measurements of three intermediate-mass subgiants from Lick and Keck Observatories. All three stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits. We find a planet with a minimum mass of 2.5 Mjup in a 351.5 day orbit around HD 192699, a planet with a minimum mass of 2.0 Mjup in a 341.1 day orbit around HD 210702, and a planet with a minimum mass of 0.61 Mjup in a 297.3 day orbit around HD 175541. Stellar mass estimates from evolutionary models indicate that all of these stars were formerly A-type dwarfs with masses ranging from 1.65 to 1.85 Msun. These three long-period planets would not have been detectable during their stars' main-sequence phases due to the large rotational velocities and stellar jitter exhibited by early-type dwarfs. There are now 9 "retired" (evolved) A-type stars (Mstar > 1.6 Msun) with known planets. All 9 planets orbit at distances a \geq 0.78 AU, which is significantly different than the semimajor axis distribution of planets around lower-mass stars. We examine the possibility that the observed lack of close-in planets is due to engulfment by their expanding host stars, but we find that this explanation is inadequate given the relatively small stellar radii of K giants (Rstar < 32 Rsun = 0.15 AU) and subgiants (Rstar < 7 Rsun = 0.03 AU). Instead, we conclude that planets around intermediate-mass stars reside preferentially beyond ~0.8 AU, which may be a reflection of different formation and migration histories of planets around A-type stars.

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arXiv2007

New Planets around Three G Dwarfs

Doppler velocity measurements from the Anglo-Australian Planet Search reveal planetary mass companions to HD23127, HD159868, and a possible second planetary companion to HD154857. These stars are all G dwarfs. The companions are all in eccentric orbits with periods ranging from 1.2 to >9.3yr, minimum (M sin i) masses ranging from 1.5 to >4.5 Mjup, and semimajor axes between 1 and >4.5 AU. The orbital parameters are updated for the inner planet to HD154857, while continued monitoring of the outer companion is required to confirm its planet status.

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arXiv2006

An Eccentric Hot Jupiter Orbiting the Subgiant HD 185269

We report the detection of a Jupiter-mass planet in a 6.838 day orbit around the 1.28 solar mass subgiant HD 185269. The eccentricity of HD 185269b (e = 0.30) is unusually large compared to other planets within 0.1 AU of their stars. Photometric observations demonstrate that the star is constant to +/-0.0001 mag on the radial velocity period, strengthening our interpretation of a planetary companion. This planet was detected as part of our radial velocity survey of evolved stars located on the subgiant branch of the H-R diagram--also known as the Hertzsprung Gap. These stars, which have masses between 1.2 and 2.5 solar masses, play an important role in the investigation of the frequency of extrasolar planets as a function of stellar mass.

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arXiv2006

Measurement of the Spin-Orbit Alignment in the Exoplanetary System HD 189733

We present spectroscopy of a transit of the exoplanet HD 189733b. By modeling the Rossiter-McLaughlin effect (the anomalous Doppler shift due to the partial eclipse of the rotating stellar surface), we find the angle between the sky projections of the stellar spin axis and orbit normal to be lambda = -1.4 +/- 1.1 deg. This is the third case of a ``hot Jupiter'' for which lambda has been measured. In all three cases lambda is small, ruling out random orientations with 99.96% confidence, and suggesting that the inward migration of hot Jupiters generally preserves spin-orbit alignment.

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arXiv2006

A Long-Period Jupiter-Mass Planet Orbiting the Nearby M Dwarf GJ849

We report precise Doppler measurements of GJ849 (M3.5V) that reveal the presence of a planet with a minimum mass of 0.82 Mjup in a 5.16 year orbit. At a = 2.35 AU, GJ849b is the first Doppler-detected planet discovered around an M dwarf to orbit beyond 0.21 AU, and is only the second Jupiter mass planet discovered around a star less massive than 0.5 Msun. This detection brings to 4 the number of M stars known to harbor planets. Based on the results of our survey of 1300 FGKM main--sequence stars we find that giant planets within 2.5 AU are ~3 times more common around GK stars than around M stars. Due to the GJ849's proximity of 8.8 pc, the planet's angular separation is 0."27, making this system a prime target for high--resolution imaging using adaptive optics and future space--borne missions such as the Space Interferometry Mission. We also find evidence of a linear trend in the velocity time series, which may be indicative of an additional planetary companion.

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arXiv2006

The Search for an Atmospheric Signature of the Transiting Exoplanet HD 149026b

HD 149026b is a short-period, Saturn-mass planet that transits a metal-rich star. The planet's radius, determined by photometry, is remarkably small compared to other known transiting planets, with a heavy-element core that apparently comprises ~70% of the total planet mass. Time-series spectra were obtained at Keck before and during transit in order to model the Rossiter-McLaughlin effect. Here we make use of these observations to carry out a differential comparison of spectra obtained in and out of transit to search for signatures of neutral atomic lithium and potassium from the planet atmosphere. No signal was detected at the 2% level; we therefore place upper limits on the column density of these atoms.

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